Studies have been designed to explore the psychobiology of cognition in man. This research attempts to interrelate psychological and biological determinants of various components of cognition such as the specific and discrete psychobiological mechanisms that define the acquisition, processing, consolidation and retrieval of experience. Experiments are designed to examine the changes in cognitive processes in response to pharmacological and behavioral manipulations, as well as in patient groups with impairment in cognition. Some of these studies have examined whether drugs that enhance aspects of cognition would reverse cognitive disturbances in patients. Findings include the cognitive changes (encoding, memory, retrieval) that occur in response to drug treatments that alter the activity of cholinergic and noradrenic central nervous system activity in patients with various psychiatric disorders and normal controls. Cognitive changes produced by neuropeptides in depressed patients and controls have also been evaluated. The structure and determinants of cognitive impairments are examined and contrasted in patients suffering from various forms of dementia.